The invention concerns a device intended to prevent the dangerous consequences of the failure of a blade of an axially rotating machine, particularly the blower of an aircraft turbojet engine.
International regulations concerning the safety of aircraft are imposing severe technical limitations on engine and aircraft designers. They stipulate specifically that the fragments ejected as the consequence of the failure of a blade of a turbojet engine must be retained within the housing of the machine so that their radial ejection will not damage vital elements of the aircraft and risk injury to the passengers. For the engines of the first generation, the designers had to prove by means of experiments truly representative of operating conditions that the structure of the engine was capable of absorbing the kinetic energy of rotor fragments ejected as a result of the failure of a blade or disc. This requirement led to the provision of sheathing at the most critical rotor locations. This mode of protection is no longer adequate for advanced engines and particularly for the dual flow engines of the most recent generation. In the latter, certain blading has acquired large dimensions and thus a large mass. The kinetic energy of a broken blade has become considerable and the sheathing necessary to absorb it would have a prohibitive weight. Further, it has become absolutely necessary to prevent damage by a broken blade to two whole blades, because the imbalance would rapidly exceed the mechanical strength of the fastenings of the engine and the latter could be torn from its supports. In this respect, the rupture of a blade with a top bead in the turboblower which often forms the first stage of the compressor of a turbojet engine may prove to be particularly dangerous because of the mass and the mechanical strength of said blade.